The present invention relates generally to an electroluminescent display, and more particularly to an electroluminescent display integrated into a dimmable mirror.
Electroluminescent displays generally comprise a plurality of elongated, generally parallel outer electrodes generally perpendicular to a plurality of elongated, generally parallel inner electrodes spaced inwardly from the outer electrodes. An electroluminescent material, such as phosphor, is sandwiched between two dielectric layers and positioned between the outer electrodes and the inner electrodes. The entire structure is then encased between two panes of glass.
Each portion of the electroluminescent material where the inner and outer electrodes overlap forms single pixel. As is well known, activation circuitry sequentially places a voltage on each of the inner electrodes. While each of the inner electrodes is activated, selected ones of the perpendicular outer electrodes are activated with either an opposite or a ground potential. As is well known, the change in potential difference across the phosphor causes the phosphor between the activated inner electrode and the selected activated outer electrodes (selected pixels) to emit light. The next inner electrode is then activated, along with other selected ones of the outer electrodes to illuminate the next row (or column) of pixels. The pixels in the electroluminescent display are thus rapidly "scanned" to provide an image which appears continuous. The outer electrodes are manufactured of a transparent conductive material, such that the light emitted by the phosphor is visible through the front of the display.
The intensity of light emitted from an ELD can be controlled by modifying the magnitude of the change in potential difference across the electrodes, i.e. a greater change in potential difference will produce a higher intensity light. Further, the intensity of the light may also be controlled by varying the duration of the voltage pulse applied to each pixel. Further, the light intensity of an ELD may also be controlled by altering the scan or "refresh" rate of the ELD, e.g. increasing the refresh rate of the ELD will increase the light intensity emitted from the ELD. To some extent these methods can be used to dim an ELD in a vehicle, such as at night or in low light conditions. However, the magnitude of the change in potential difference can only be decreased down to a certain threshold below which the electroluminescent material will not generate light at all. Further, decreasing the refresh rate below a certain threshold results in noticeable unpleasant screen "flicker." Further, reducing the light intensity emitted from the ELD beyond a certain point causes any existing screen image "burned into" the ELD to become prominent.
Mirrors, such as sideview or rearview mirrors in a vehicle, are increasingly including integrated displays. Typically the display is located in a non-mirrored portion of the mirror, in which the mirror material is etched and does not provide a mirror appearance. Other mirrors include a plurality of LEDs generating light of a specific wavelength positioned behind a mirror surface which is specially coated to transmit light of the specified wavelength. Heretofore, however, an ELD has not been integrated into a mirror to selectively provide a mirrored appearance or the electroluminescent display.